Many portable equipments, including cellular phones, has a key switch in the operating section. These portable equipments have a depression-judgment apparatus for detecting whether a key switch is depressed or not.
A depression-judgment apparatus of the conventional art will be described in reference to FIG. 3. FIG. 3 is a block diagram showing the configuration of a depression-judgment apparatus of the conventional art. In FIG. 3, a reference numeral 1 denotes a key switch, a reference numeral 300 denotes a depression-judgment apparatus and a reference numeral 8 denotes a central processing unit (hereinafter referred to as CPU). Depression-judgment apparatus 300 comprises a power supply terminal 3, an input terminal 4, a ground terminal 11, a resistor 12, a depression-judgment circuit 6 and an output terminal 7.
The operation of a depression-judgment apparatus of the conventional art configured as above-mentioned will hereinafter be described. In a depression-judgment apparatus of the conventional art, input terminal 4 becomes high level when key switch 1 is in OFF status, and depression-judgment circuit 6 (for example, comprised of flip-flops) would not operate, outputting low level from output terminal 7. Furthermore, when key switch 1 is in ON status, input terminal 4 becomes low level, and depression-judgment circuit 6 operates and detects that a key switch is depressed, outputting a high level from output terminal 7 so as to inform depression. As mentioned above, in a case where key switch 1 is depressed and hence changes from OFF to ON, input terminal 4 changes from high level to low level, and output terminal 7 of depression-judgment circuit 6 changes from low level to high level.
Depressed key detecting method in accordance with patent document 1 detects chattering characteristics which varies due to differences in intensity of key depressions.
However, in the conventional configuration, chattering occurs when key switch 1 is depressed and changed from OFF to ON, and input terminal 4 thereby changes from low level to high level. Since the level of input terminal 4 would not settle due to chattering, the conventional apparatus had a problem in which depression-judgment circuit 6 does not properly detect that key switch 1 is depressed, and hence depression-judgment apparatus cannot conduct a proper depression-judgment.
The present invention purports to solve the above-mentioned conventional problems, and aims to provide a depression-judgment apparatus which properly judges the ON/OFF of a key switch without being affected by chattering that occurs when key switch is turned ON.
The present invention aims to provide a depression-judgment apparatus having a still lower power consumption.
The present invention aims to provide a depression-judgment apparatus capable of setting a key switch detection cycle from an outside, corresponding to key switch characteristics and/or key switch detection velocity which is required.